What is a tribe?

a group of people, often of related families, who live together, sharing the same language, culture, and history, especially those who do not live in towns or cities:
— a tribe of Amazonian Indians;
— the Masai tribe.

informal a large family or other group that someone belongs to.

Wikipedia says:

A tribe is viewed, developmentally or historically, as a social group existing before the development of, or outside, states. A tribe is a group of distinct people, dependent on their land for their livelihood, who are largely self-sufficient, and not integrated into the national society.

All of these definitions are talking about the traditional meaning, which is true mostly for underdeveloped societies. Recently, we have been witnessing the human evolution from the tribal to mass society. This is a consequent step of progress because of technology development and ease of connection. We have no boundaries in collaboration and communication within the world. But now we can see, that in a modern pattern of existence human being experiencing a lot of difficulties, as for millions of years we lived in a small bonded groups, and now, in the one global society, more and more people feel lonely and isolated. That is why there is a place for the next step of evolution.

As groups based on the actual or perceived kinship and descent are not effective in the current society, and human beings can not live as one global community, they are looking for other factors, which connect them. In the 1980s, French sociologist Michel Maffesoli coined the term “urban tribes” to describe small groups of people defined by shared interests and lifestyle preferences around which modern societies are organized. Today in the concrete jungles that are our contemporary megacities, there is a need to stick together.

Nowadays, we can see loads of different neo-tribes, based on sometimes extraordinary interests: